The Max Units field represents a resources maximum capacity to work on assigned tasks. Specifying a Max Units of 100% means that 100% of that resource’s working time is available to work on assigned tasks within the project plan. Project will notify you with an indicator if a resource is assigned to more work than the resource can accomplish. For example, if a resource is assigned to two tasks at 100% capacity that start on the same day and require 8hrs a work each day per task the resource will be overallocated. For Resources that represent a specific role you may specify a Max Units value that is larger to indicate how many people with that role are available. For example, if you have 5 developers and you create a Generic resource called Developer the Generic may be assigned a Max Units value of 500%.
This topic discusses entering and adjusting resource Max Units, and when to use specify values other than 100% to account for part-time resources and operational work.